On Thu, 19 Aug 2010 10:58:25 -0400 Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote: > On Thu, 2010-08-19 at 10:37 -0400, Christoph Hellwig wrote: > > On Thu, Aug 19, 2010 at 10:15:25AM -0400, Jeff Layton wrote: > > > I'm looking at backporting some upstream changes to earlier kernels, > > > and ran across something I don't quite understand... > > > > > > In nfs_commit_unstable_pages, we set the flags to FLUSH_SYNC. We then > > > zero out the flags if wbc->nonblocking or wbc->for_background is set. > > > > > > Shouldn't we also clear it out if wbc->sync_mode == WB_SYNC_NONE ? > > > WB_SYNC_NONE means "don't wait on anything", so shouldn't that include > > > not waiting on the COMMIT to complete? > > > > I've been trying to figure out what the nonblocking flag is supposed > > to mean for a while now. > > > > It basically disappeared in commit 0d99519efef15fd0cf84a849492c7b1deee1e4b7 > > > > "writeback: remove unused nonblocking and congestion checks" > > > > from Wu. What's left these days is a couple of places in local copies > > of write_cache_pages (afs, cifs), and a couple of checks in random > > writepages instances (afs, block_write_full_page, ceph, nfs, reiserfs, xfs) > > and the use in nfs_write_inode. It's only actually set for memory > > migration and pageout, that is VM writeback. > > > > To me it really doesn't make much sense, but maybe someone has a better > > idea what it is for. > > > > > + if (wbc->nonblocking || wbc->for_background || > > > + wbc->sync_mode == WB_SYNC_NONE) > > > > You could remove the nonblocking and for_background checks as > > these impliy WB_SYNC_NONE. > > To me that sounds fine. I've also been trying to wrap my head around the > differences between 'nonblocking', 'for_background', 'for_reclaim' and > 'for_kupdate' and how the filesystem is supposed to treat them. > > Aside from the above, I've used 'for_reclaim', 'for_kupdate' and > 'for_background' in order to adjust the RPC request's queuing priority > (high in the case of 'for_reclaim' and low for the other two). > Ok, I don't really have a great way to test the above change though aside from sticking it into the backport I'm working on for RHEL5 (2.6.18). I suspect that the existing flag checks probably cover a lot of the WB_SYNC_NONE cases already. Changing it to a check for WB_SYNC_NONE would help me as RHEL5 doesn't have the for_background flag... Cheers, -- Jeff Layton <jlayton@xxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>